Participation in studies covered under this project are predominantly confined to data analysis, interpretation and manuscript preparation for results collected outside the NIA IRP, through long-standing collaborations with a number of extramural investigators. During the current funding period these activities have focused predominantly on research examining the morphological effects of estrogen deficiency and treatment on synaptic markers in the hippocampus and dorsolateral prefrontal cortex in young and aged monkeys. Providing a window on the functional significance the observed effects, all results are evaluated in relation to the cognitive influence of hormone manipulation assessed in the same subjects. In overview, current results from this project indicate that both the hippocampus and prefrontal cortex regions are sensitive to ovarian hormone regulation in the aged monkey brain. The mechanisms mediating this regulation, and their relationship to the cognitive outcome of aging, appears to be regionally selective.